Device malfunction in endovascular treatment of intracranial aneurysms: shared responsibilities of physician and manufacturer.

. . . the war is too important to leave it to the generals, the medicine is too important to leave it to the doctors, the science is too important to leave it to the scientist. . . In this issue of the AJNR, Kwon et al describe “technical problems associated with new designs of Guglielmi Detachable coil [GDC]”; namely, device malfunction, such as the spontaneous detachment of GDC coils, coil backsliding into the microcatheter, and protrusion of small proximal parts of coils into the parent vessels after detachment. Only 12 events were reported out of many coils inserted. Unfortunately, the exact number of total coils used is not provided. Kwon et al reported these events in 10 (14.5%) of 69 recently treated patients. None of those patients had an adverse clinical outcome after endovascular treatment. The authors propose that the malfunctions they encountered are associated with the new SynerG GDC system (Boston Scientific/Target, Fremont, CA), particularly with the subtype, the stretch-resistant SR. Other complications, such as thromboembolism, aneurysmal rupture, coil migration, and coil stretching, were excluded from this report. The authors present a nonstandard in vitro evaluation of both the GDC system and the new SynerG GDC system in which they used different coils (3D, 2D, SR, Soft, Ultrasoft). Manual force was used to bend and fracture the coils during placement in an aneurysmal model rather than by using mechanical testing systems to quantify the force. Coil jamming within the delivery system was also explored. The authors provide some elegant solutions for overcoming these problems in the clinical setting. The major goal of the SynerG GDC system is to reduce the detachment time from several minutes, with the standard GDC system, to a few seconds, with the SynerG, thus reducing the overall procedural time. As the authors describe in detail, this reduction is achieved by the manufacturer’s modification of the detachment zone. Figures 1 and 2 illustrate the major differences between the old and the new system. Two major forces are involved with coil malfunction, and an experienced interventionalist appreciates the difference: 1. The force required to push a coil into the aneurysm is generally high and increases with the amount of coils already placed in the aneurysm. This force, F1, can also be high if coils are pushed through an extremely tortuous vascular system because of increased intracatheter friction. F1 is transmitted through the pusher wire to deploy the coil, but the force is also transmitted to the weakest area of the coil system, which is the detachment zone (Figs 1 and 2), if the coil meets resistance. This may cause the bending or fracturing of the detachment zone as well as a subsequent premature coil detachment within the catheter or the aneurysm. The force required to fracture the coil within the delivery catheter is higher than is the force exerted during intraaneurysmal coil placement, because the coil is confined within the catheter, and no deflection occurs. A broken coil can be pushed out of the delivery system, depending on the inner lumen of the catheter. An overlapping of the coil pusher and the proximal segment of the coil may occur, depending on the relation of the inner lumen of the catheter to the coil diameter used; this will increase the deployment force. 2. If a coil is pulled back for whatever reason, and caught within the aneurysm-coil mass or the delivery catheter, a stretching (unraveling) of the coil may occur. The physician recognizes the pull force, F2, the weakest of all forces. Of course, continuous stretching will ultimately lead to fracture of the coil; this requires an extremely high force followed by the sudden drop of said force. F1 and F2 highlight the vital role of the coil detachment zone and the contradictory requirements for successful coil deployment. On one hand, we require a strong junction. On the other hand, we require a quick detachment time. Some new coil manufacturers attempt to address these issues. Analysis of all the units returned to the manufacturer (Target/BSC) from clinical sites shows that the number of complaints regarding GDC performance over the past 5 years can be summarized as follows: Confirmed unintentional detachment or breakage (% of units sold): 1997: 0.06% 1998: 0.05% 1999: 0.02% 2000: 0.02% 2001: 0.03% In addition, the “spontaneous coil detachment” failure mode exemplified by the broken core wire that was reported to have occurred five times in Kwon et al’s investigation has been confirmed to have occurred in fewer than 3% of the GDC centers worldwide. This figure is based on field returns to the manufacturer during 2001. Editorials